1. Field of the Invention
The present invention relates to an organic EL element, and to an organic EL display which utilizes the organic EL element.
2. Description of the Related Art
Organic EL elements have features such as spontaneous light emission, high-speed response, and the like, and they are expected to be applied to flat panel displays. A two-layer (laminated) organic thin film having positive hole transporting properties (positive hole transporting layer) and organic thin film having electron transporting properties (electron transporting layer) has been reported (C. W. Tang and S. A. VanSlyke, Applied Physics Letters vol. 51, and 913 (1987)), and due to its large area light-emitting element which emits light at a low voltage of 10V or less, it has recently been attracting attention. Organic EL elements of the laminated type have the basic construction, positive electrode/positive hole transporting layer/light-emitting layer/electron transporting layer/negative electrode, wherein the functions of the positive hole transporting layer or electron transporting layer may be added to that of the light-emitting layer as in the two-layer type.
It is expected that organic EL elements will soon be applied to full color displays. In this full color display, it is necessary to have pixels emitting light of three primary colors, blue (B), green (G) and red (R) arranged on the panels. There are three methods for achieving such arrangements;    (a) providing three types of organic EL elements, blue (B), green (G), red (R),    (b) separating the light emission light from an organic EL element emitting white light (which is a mixture of blue (B), green (G) and red (R) light) by color filters,    (c) converting the light emission from an organic EL element emitting blue light into green (G) and red (R) light emission by a color conversion layer using fluorescent light.
In all of these systems, blue (B) light emission is indispensable, so it is desirable to provide an organic EL element of high luminance, high efficiency and high color purity which emits blue light.
As an example of an organic EL element emitting blue colored light, an organic EL element using pyrene, which is a type of aromatic condensed ring compound, or an alkyl derivative or cycloalkyl derivative thereof as a luminescent material, has for example been disclosed in Japanese Patent Application Laid-Open (JP-A) No. 09-241629. However, as the fluorescence quantum yield in this luminescent material was small in this organic EL element, there was a problem in that the purity of blue light emission was not sufficient. JP-A No. 2001-118682 proposes an organic EL element showing blue fluorescence of high color purity, and in particular a large fluorescence quantum yield, using 1,3,6,8-tetraphenylpyrene and its derivatives (the fluorescence quantum yield of 1,3,6,8-tetraphenylpyrene is as high as 0.9 compared to the fluorescence quantum yield of an unsubstituted pyrene which is 0.3). However, in this organic EL element, there is a problem in that EL properties, i.e., the light-emitting luminance, the light-emitting efficiency, color purity, and the like, are not sufficient, and further improvements are desirable.
To obtain an organic EL element of high light-emitting efficiency, an organic EL element which has a light-emitting layer showing high light-emitting efficiency, a small amount of a pigment molecule having high fluorescence light emission properties is doped as a guest material into a host material which is the main component, is proposed in C. W. Tang, S. A. VanSlyke, and C. H. Chen, Applied Physics Letters vol. 65, and 3610 (1989). Example 9 in JP-A No. 11-312588 discloses tetraphenylpyrene as the guest material in 9,10-di(3′,5′-o-tolyl)phenylanthracene as the host material in the aforementioned light-emitting layer. However, in this case there was almost no effect of doping the tetraphenylpyrene, and the light-emitting luminance and color purity were also insufficient.